About three weeks later, on April 14, Philip Markoff—a tall, blond, 23-year-old med student at Boston University—came across an Erotic Services ad on Craigslist posted by 26-year-old Bronx-based call girl Julissa Brisman. Markoff sent her an e-mail, and the two arranged a soiree at the Marriott Copley Hotel in Boston's upscale Back Bay district. Seconds after entering the room, Markoff allegedly pounced on Brisman, who, according to a medical examiner, fought back tenaciously. Markoff stands accused of shooting Brisman three times—twice in the torso, once in the hip—killing her.

Markoff was with his then-fiancee on their way to Foxwoods Casino in Connecticut when he was pulled over and arrested just south of Boston on I-95. The summa cum laude graduate of the State University of New York-Albany was later implicated in a similar Boston robbery, as well as one in Warwick, Rhode Island. A common thread ran through all three crimes: young women solicited through Craigslist's Erotic Services category.

Even more than the Weber slaying, the Markoff murder captured the public imagination. How could somebody like Markoff—clean-cut, well-educated, ambitious and in the midst of planning a beachside wedding this summer—do such a thing? Lacking any other hook, the national press dubbed Markoff "the Craigslist Killer," a phrase that still makes Newmark and Buckmaster cringe.

"We're taken aback any time we hear that term used," says Buckmaster. "Although, if you stop and think about it, it's a testament to how exceedingly rare violent crime is on Craigslist, when you consider that it's the most common way that Americans are meeting each other these days by a significant margin. The reason they don't call him 'the Handgun Killer' or 'the Boston Killer' or 'the Hotel Killer' is because thousands of homicides have involved those factors."

The Weber and Brisman murders couldn't have come at a worse time for Craigslist. Just as the crimes were splashing into primetime-news segments, a sheriff in Chicago was mounting a campaign against the company.

Cook County Sheriff Tom Dart first made headlines in October when he announced he was suspending all foreclosure evictions in his jurisdiction. The energetic state representative-turned-sheriff was fed up with throwing law-abiding people out on the streets.

By March, Dart was onto a new cause: Craigslist. He filed a federal lawsuit against the site, accusing it of "facilitating prostitution." He claims that, during the past two years, his department has arrested more than 200 Craigslist users on charges ranging from prostitution to juvenile pimping and human trafficking.

"In the hundreds of arrests that we've made, never have we had one where we went under the guise that it's a massage and it turned out that it was just a massage," says Dart. "We know what's going on."

Despite Dart's confident tone, most legal experts believe his lawsuit has little chance of success—a clause in the Communications Decency Act immunizes websites from liability for content posted by third parties. The goal is to ensure robust free speech, says Matt Zimmerman, an attorney with the Electronic Frontier Foundation. "We don't want to have to make websites actively monitor what goes on because that would drive up costs, and you would have every site saying, 'You know what, it's not worth it; we're not going to allow people to talk to each other at all.'"

A far more imposing threat to Craigslist is Blumenthal, who resurfaced in an April 22 open letter with additional, more sweeping demands. Blumenthal implored Craigslist to, among other things, disallow salacious prostitution-themed search terms, hire staff to monitor for pornographic images and ads, and eliminate the Erotic Services category altogether.

"We felt the first agreement was a good first step, but insufficient," says Blumenthal. "The prostitution ads have continued; the pornography is still there. It has failed to accomplish all that we'd hoped."

Buckmaster says Craigslist welcomes the "constructive criticism" and confirms that the two sides are in the midst of hashing out a voluntary agreement. But don't expect Craigslist's most popular and controversial category to go away any time soon.

"We added the Erotic Services category some years ago at the request of users who had been seeing those ads posted throughout our personals and services categories and wanted to see them collected in one space and put behind a warning screen," says Buckmaster. "And having them in one place has allowed them to be monitored more closely, by both our staff and law enforcement."

Others in the online-classifieds trade back Buckmaster's assessment. Carl Ferrer, co-founder of Backpage.com, Village Voice Media's online classifieds partner, points out that even if Blumenthal's demands were met, it wouldn't safeguard against people posting it elsewhere.

"If you eliminate Erotic Services, the content will just migrate to Miscellaneous Services and other categories," Ferrer says. "Then it becomes a whack-a-mole strategy."

There's also no evidence that overall rates of prostitution or murder have increased in correlation to Craigslist's ascension, says the AIM Group's Zollman. "There have always been hookers. There have always been people who sell drugs and other illegal things. But to call these 'Craigslist-related crimes' is no fairer than calling car accidents 'GM-related deaths.'"